Don't lock state if we don't actually need access to state

[sornas]

Sometimes we use an Arc<Mutex<State>> as a way of passing around fields that are completely separate from other parts of the state. These should be reworked since they are potential deadlocks as well as a bit too close to monolithic.

The following is an example but more such locks probably exist.

Originally posted by @sornas in https://github.com/mum-rs/mum/pull/58#discussion_r553223424